The present invention relates to methods of controlling an industrial robot compensate for a disturbance in the control of the robot's motion due to a mechanism of the robot's effector.
In order to cause a robot to perform operations such as boring, deburring, and grinding a manufactured site, the robot is required to have high performance which the conventional positioning robot does not have. One of the required performance items is to control a force applied to an object. To this end, the conventional techniques have proposed a method of controlling such force, using hardware, that is, a mechanism which sets rigidity in a robot's effector and a method of controlling such force, using software, that is, a technique which provides mechanical compliance for a robot by control software. Namely, any one of those methods is capable of providing compliance for the robot's effector. The latter method is capable of providing contact force control over the motion of the robot as opposed to the former method. In particular, a method of realizing a mechanical compliance mechanism of multiple degrees of freedom in the robot's effector by utilizing software is described as "virtual compliance control of multiple degree of freedom robot" in Society of Instrument and Control Engineers, Collection of Papers, Vol. 22, No. 3, pp.343-350, March 1986.
The virtual compliance control is characterized in that the mechanical compliance of the robot's effector is set at a desired value for an external force and hence the robot has mechanical compliance for an object.
It is impossible to directly measure the value of an external force required for actual construction of this control system between the robot's effector and the object. Thus, it is usually measured at a robot's wrist between the robot's body and its end effector. It is to be noted that the value of a measured external force to be described in more detail later includes an external force involving a physical parameter of the end effector. It is impossible for the robot to have any mechanical compliance for the object unless (1) the external force involving a physical parameter of the end effector is accurately calculated, and (2) the calculated external force is subtracted from a measured value of the external force to obtain the value of the external force from the genuine object.
In order that the robot is provided mechanical compliance for an object, the measured value of the external force conventionally was taken apart from the weight of the end effector itself as an external force due to the physical parameter of the robot's end effector on the external force.
However, when a rotational body having a mechanically large rotational momentum is set as an end effector, the weight of the above-mentioned end effector itself as well as a gyro moment occurring due to interference of the rotational momentum of the end effector and the robot's momentum must be reflected on the external force in order that the robot has any mechanical compliance for the object.
In the conventional virtual compliance control, no gyro moment has been reflected on the external force. Thus, when a rotational body having a mechanically large rotational momentum is set as an end effector, an external force component of a gyro moment occurring due to interference of the rotational motion and the robot's motion prevails among the external force components, so that an effective control system cannot be constructed as the case may be.